Mercury-wetted relay and method of manufacture

ABSTRACT

A mercury-wetted contact capsule used in relays or switch assemblies whose contacts are hermetically sealed in a chosen environment and includes a flat, spiral spring armature. The construction permits use of an optimum mercury film supply affording long operating life, elimination of contact bounce, chatter and noise, and operation in any position. The concentric symmetry design facilitates manufacture by a special preassembly and assembly sequence that ensures precise control of mercury film maintenance and exact parts positioning, and can be readily automated even for subminiature sizes.

United States Patent 51 Zimmer 1 Feb. 15, 1972 [54] MERCURY-WETTED RELAY AND 2,288,811 7/1942 Leveridge ..335/58 METHOD OF MANUFACTURE Primary Examiner-Harold Broome [72] Inventor John Zmumr waynesbom AttorneyMichael Masnik, Frank L. Neuhauser, Oscar B.

[73] Assignee: General Electric Company Waddell and Joseph B. Forman [22] Filed: Oct. 5, 1970 [57] ABSTRACT [211 78042 A mercury-wetted contact capsule used in relays or switch assemblies whose contacts are hermetically sealed in a chosen [52] U.S. Cl ..33S/58 environment and includes a flat, spiral spring annature. The

[5 Int. Cl. construction use of an optimum mercury upply [58] Field of Search ..335/58, 57,47, 55, 196, 154 affording long operating life, elimination of Contact bounce,

chatter and noise, and operation in any position. The concen- [56] Rem-mes tric symmetry design facilitates manufacture by a special UNITED STATES PATENTS preassembly and assemhly sequence that ensures precise control of mercury film maintenance and exact parts positioning,

........................... and can be automated even for ubminiature sizes 3,331,040 7/1967 Woodhead ..335/l96 2,445,406 7/1948 Pollard, Jr. ..335/58 15 Claims, 8 Drawing Figures PATENTEUFEB 15 m2 3.643.185

SHEET 1 BF 3 PLATINUM (a) DISK Hg) WETTABLE WELDED T0 (T0) DISK TANTALUM (T0)DISK (NON Hg WETTABLE) INVENTOR. JOHN S. ZIMMER BY GROOVED PASSAGE 7 7M 7% FOR GAS FLUSHING HIS ATTORN EY MERCURY-WE'ITED RELAY AND METHOD OF MANUFACTURE BACKGROUND OF THE INVENTION Relays and switches of the mercurywetted contact type have long been known for their good operating-cycle life and relative freedom from contact bounce, these and other advantages largely stemming from the fact that the constantly renewed mercury contact film surface resists spark deterioration, improves dry-circuit (low current) circuit integrity, and provides a mechanical damping that reduces bounce and chatter even with very small and low-inertia moving parts. Principal disadvantages of such relays have been the necessity for compromises between providing an adequate mercury supply over long periods and the difficulties (bridging of insulating parts) if an excess of mercury is provided. The latter difficulty also tends to make the devices position sensitive. The necessity for accurate gauging of the quantity of free mercury maintained in a reservoir or pool has made many designs unduly expensive, and prevented automated assembly; moreover, in those designs which eliminate the mercury pool reservoir, and rely on capillary action for mercury film maintenance, gradual failure of the supply has tended to vitiate the long life expectancy predicted by theoretical considerations.

SUMMARY OF THE INVENTION The contact assembly cell or capsule is essentially of concentric or cylindrical symmetry fabricated of circular or tubular subassemblies which inherently ensure precise positioning of the parts, including the contact spacing determinants and the free volume of the contact chamber. Special treatment of certain of the parts for control of mercury wettability permits exact gauging of the supply of mercury for permanent optimization of the mercury film without any pool or excess. Provision of the desired gaseous atmosphere, preferably hydrogen gas, is facilitated in that conventional outgassing and sealing off machinery can be utilized, as in miniature lamp manufacture.

In brief, the preferred embodiment of the relay comprises a central moving contact element in the form of a thin, springy and magnetically permeable conductive disc carrying central and opposed contact buttons which face toward spaced, coaxial fixed contacts in the form of wires (preferably platinum wires) that pass centrally and axially through respective magnetically permeable tubes forming inner magnetic cores adapted to receive respective windings. The major surfaces of the contact disc and its contact buttons, are mercury wetted, as are the tips only of the contact wires that cooperate with the contact buttons. The inner magnetic cores are ceramic (glassto-metal) sealed adjacent their facing ends within respective outer tube sections, and the coaxial subassembly of inner tubular core, ceramic-to-metal seal, and outer tube section forms at one end of the subassembly a major wall face of a generally ring-shaped hermetic capsule divided symmetrically across its central axis by the moving contact disc.

The flexible contact carrying disc is held about its margins between a pair of magnetically permeable flat-faced annular rings engaging the outer margins of both disc surfaces, and these parts are clamped in position by the core subassemblies, one on each side in the case of a single-pole double-throw contact configuration in a cylindrical assembly. The inner faces of the rings, which form the peripheral wall of the contact chamber, are wet by mercury to form a precise reservoir supply of mercury without a physical pool thereof. An outer metallic sleeve surrounds the entire unit, and is ultimately welded to the ends of the outer tube sections. This hermetically closes off the contact chamber, except for the gas or exhaust passages through the tubular inner magnetic cores, through which passages pass the fixed contact wires in close but not gastight relation. The wires are mechanically held in place by crimping thereon the outer, preferably necked-down, ends of the inner tube sections. The latter, therefore, provide gas passages into and out of the contact chamber allowing air to be removed, and, if desired, another gas such as hydrogen under suitable pressure, to be supplied to the chamber after which the tube section ends are hermetically welded shut to complete the unit. The cylindrical spaces between each inner tube section and the surrounding outer tube sections may receive coil windings.

In the description which follows, the term wet by mercury refers to a surface which is wettable by mercury, or by any similar electrically conductive liquid, and which is in fact wetted by a film of the mercury applied thereto. Wettability may be inherent in the material of which the surface is a boundary or may be imparted (or prevented) in other cases by appropriate surface treatment, plating or cladding, as will appear. The term magnetic" applied to materials refers to those whose magnetic permeability is substantially greater, or many times greater, than that of air; for example, mild iron or steel. No permanent magnetization or high degree of remanence is intended to be implied by the unqualified term magnetic." The terms proximal and distal, used in referring to the opposite ends of the inner tubular cores and their contact wires, refer to the ends that are close (proximal) to or within the contact chamber facing the opposite major faces of the flexible springy contact disc, and those other ends which are remote (distal) from the contact chamber.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a central, axial section taken through the length of a preferred and typical form of capsule according to the invention showing open, single-pole double-throw contacts (SPDT).

FIG. 2 is a similar view, to a larger scale, of slightly more than one-half of the structure of Fig. 1.

FIG. 3 is a plan view of a preferred form of flexible, flat, spiral spring contact armature or disc.

FIGS. 4-7 illustrate use of capsules embodied in various circuit arrangements.

FIG. 8 illustrates an alternative method of constructing the stationary capsule contact.

DESCRIPTION OFA PREFERRED EMBODIMENT The general relationship, construction and manner of assembly of a relay in accordance will best be understood from FIG. 1 of the drawings. As there shown, the central flexible contact armature is indicated at numeral 10 having attached, as by welding, centrally of each of its major circular faces a contact button 12, 14, preferably of platinum, which is wettable by mercury. The armature itself is made of magnetic material, such as soft iron, and the entire assembly after the contact buttons are in place is mercury wettable.

The flexible disc 10 is secured in place by having its peripheral margin clamped between two flat-faced annular rings l6, 18 of magnetic material. Where mercury wettable operation is involved, at least the inner cylindrical faces of the rings are platinum plated to confer wettability; for convenience, the entire ring surfaces are so plated. When the inner ring surfaces and the surfaces of disc 10 are wet by mercury, the ring surfaces provide a calibrated reservoir (but not a pool) of mercury which is fed by capillarity across the disc faces and to the contact buttons 12 and 14.

The magnetic rings 16 and 18 are clamped to the disc by respective outer sleeves or tube sections 20, 22 which may or may not be magnetic according as the design calls for a magnetic return path for the core flux or an outer (leakage) air path. In one embodiment, the sections were metallic to permit metal-toglass sealing. Coaxial with each of the outer tube sections is a magnetic inner tubular core section 24, 26, respectively, held in place by a ceramic button, such as glass, 28 or 30 which forms a glass-to-metal" seal with the inner tube section '(24) and the corresponding outer tube section 20, thus forming respective subassemblies as will appear.

Within each of the inner tubular core sections passes a contact wire 32, 34, preferably of platinum, which has previously been chromium plated to renderit nonwettable by mercury, the proximal ends of these wires (adjacent the contact buttons 12 and 14) being cut off to expose bare platinum metal which is inherently wettable by mercury. The proximal faces of the inner core tube sections have welded thereon respective thin annular washers 36, 38 (FIG. 2) of tantalum or the like to inhibit wettability by mercury. The wires 32, 34 pass rather loosely through the bores of the inner core section tubes, the clearance being exaggerated in FIG. 2 but sufficient to allow passage of gases during the purging and filling operations. The outer end of each inner tube section 24, 26 is necked-down and physically crimped as at 40 and 42 against the corresponding wire to secure it in position so that the proximal (contact) ends of the wires will lie precisely the desired distance from the contact buttons 12 and 14 after assembly.

The two subassemblies constituted (each) by an outer tube section, a glass-to-metal seal, and an inner tube core section with its contact wire are held clamped against the outer faces of the rings 16 and 18 by an outer overall metallic sleeve 44. The outer ends of this sleeve are welded, as at 46, to the outer ends of the tubular sections 20 and 22 to provide a hermetic seal therebetween.

FIG. 3 shows a preferred configuration for the flexible magnetic disc or diaphragm 10, the same having a circular margin and a spiral slot 48 to improve its flexibility at the center, to which (on each side) a contact button has been welded as above-described. The disc is conveniently formed by photoetching techniques well known to those skilled in the art and provides in effect a spiral spring in conductive relation to the moving contacts 12 and 14.

Upon assembly, the confronting faces of the subassemblies formed and held together by the glass-to-metal seals define the sidewalls of a complete contact chamber, whose outer wall or rim is formed by the magnetic rings 16 and 18. The surface of the glass seal within the chamber is inherently nonwettable by mercury, as is the tantalum washer 36 and the lateral surface of the plated wire 32. Thus, only the inner surfaces of rings 16 and 18, the surfaces of disc 10 and the contact buttons l2, l4 and the tip ends of the contact wires will maintain a mercury film. The small exposed lateral surfaces of cores 24 and 26 are not in mercury-flow communication with any other parts within the chamber so that the wettability of these surfaces is for most applications not material.

The normal positions of operating windings are indicated by the dot and dash outlines 50 at the right end of FIG. 1, such windings surrounding each of the inner core sections generally within the respective outer tube sections 20 and 22. Contact leads for the fixed contacts are indicated at numerals 52 and 54 and the lead for the flexible disc contact may be as at 56. Method of Assembly The cores 24 and 26 have their reduced outer ends formed by turning the tubular core stock and the tantalum washers 36 are welded to their other ends. Each core and its outer tube section (20, 22) which has been previously cut to length from tubing are glassed together in an inert gas furnace using glass preforms in the normal manner of the art. The platinum contact wires 32, 34 having previously been chrome plated are threaded through the core sections and crimped and welded in place (at 40, nonhermetically) and the contact end is cut off to expose the bare platinum only at the wire s tip.

The core assemblies, the spring disc 10 with its contact buttons, and the magnetic rings 16 and 18 are then introduced into a chamber containing an inert gas, such as argon, and a pool of mercury. The temperature of the chamber is then raised to the boiling point of mercury and wetting of the platinum surfaces takes place. After the chamber has cooled down, the parts are removed, excess mercury removed from them as by shaking, and these parts are assembled within the sleeve 44; and, the distal regions (outer ends) of the cores and the sleeve are tungsten-inert-gas welded as at 46 to form an assembly which is complete except for the final pressurization and seal-off.

To effect the final operation, hydrogen gas is flushed through one core tube from its outer end into the contact chamber and out of the other core tube. The latter end is then crimped and welded shut hermetically, as at 58, the hydrogen pressure increased to the desired level, and the other end crimped and welded shut hermetically as at 60. The entire capsule is now charged with gas and ready for operation.

The two magnetic ring spacers l6 and 18 are wet with mercury to provide a reservoir, but there is no free pool of mercury which could cause contacts to be established between the armature l0 and wires 32 or 34 otherwise than by actuation of the armature to engage the stationary contact. By capillary action the mercury keeps the contact buttons of the flexible disc constantly wet so that as the spring 10 flexes back and forth under magnetic control (of the drive coils or the like), contact is made with the tips of the platinum wires through a thin film of mercury, as desired. Mercury lost from the contacts due to vaporization or in droplets due to contact making and breaking is introduced again into the closed film system by means of the reservoir created by the two mercury-wetted magnetic rings. The contact tip of the wire 32 is replenished with mercury from the wetted button 12, for example, which in turn is replenished from the reservoir created by the two mercurywetted magnetic rings. The tip of wire 32 is made relatively small in diameter with respect to contact 12 and protrudes beyond the core and washer 36 to provide a controlled area that can be wetted. This is also true with respect to 34 and 38. This insures an amount of mercury sufficient to make good contact but without mercury bridging due to excessive mercury which would be the case if the contact tip were very large in diameter. The core 24 is made substantially larger in diameter than tip 32 and positioned close to button 12 to provide a relatively large pole face area, thereby reducing the reluctance of the magnetic circuit. To prevent the core from being wetted by mercury, it is provided with a nonwettable surface 36.

By controlling the amount of mercury introduced into the capsule as above-described, a nonposition sensitive ,device is readily achieved and one which is free from bounce and chatter and exhibits a cycle life as high as millions of operations without failure.

FIG. 4 illustrates a circuit embodiment including a capsule in the form of a center-off contact, nonpolarized, tristable single pole, double throw switch. Circuit is closed upon energization of coil B by circuit 70. In its energized state, the flux flow is as indicated by dotted line (b EM. Circuit A is closed when coil A is energized by circuit 71 and coil B is deenergized. Circuits A and B remain open, i.e., with the flexible armature l0 suspended in noncontacting position between the contact tips of 32 and 34 when coils A and B are deenergized or energized to effect offsetting equal pulls on the armature 10.

FIG. 5 illustrates a circuit embodiment including a capsule in the form of a monostable, nonpolarized single-pole, doublethrow switch. Armature 10 is mechanically biased to the right to normally contact the tip of contact 32 by the manner in which it is mounted to one side of the sealed chamber. To open circuit B and close circuit A, coil A is energized by circuit 72. In its energized state, the flux flow is as indicated by dotted line 4: EM. To open circuit A and close circuit B, coil A is deenergized.

FIG. 6 illustrates a circuit embodiment including a capsule in the form of a polarized, latching, bistable single-pole, double-throw switch. A component flux flow occurs in the circuit in response to the inclusion of a permanent magnet between the capsule wall and the outer core of the switch assembly as shown. The flux flow occurs along two paths PM as shownin dotted line. In a normal situation, in the absence of any energization of coils A and B, the armature 10 would be contacting either contact tip 32 or 34. For purposes of discussion, we shall assume that armature 10 is contacting the tip of contact 34, thereby closing circuit A and opening circuit B. To open circuit A and close circuit B, coil B is pulsed by 73 causing an additional flux flow EM. This results in the permanent magnet flux and electromagnetic flux to be additive at B and subtractive at A causing armature to contact the tip of contact 32. When power is removed from coil B, the B circuit will remain latched due to the permanent magnet flux PM flowing through the right-hand circuit of the switch, To open circuit B and close circuit A, coil A is pulsed by 74 causing an additional flux flow EM. This results in the permanent magnet flux and the electromagnetic flux to be additive at A and subtractive at B, causing armature 10 to contact the tip of contact 34. When power is removed from coil A, the A circuit will remain latched due to the permanent magnet flux PM flow through the left-hand circuit of the switch.

FIG. 7 illustrates a latched, single-pole, double-throw, manual switch. Flux flow 4) PM occursin the switch circuit in response to the inclusion of a permanent magnet between the capsule wall and the outer core of the switch assembly. Part of path includes a displaceable switch actuator 75 of magnetic material. Moving the right-hand portion of actuator 75 in the direction 76, causes armature 10 to contact the tip of contact 32 closing circuit B. The circuit remains latched in this position. Moving the left-hand portion of actuator 75 in the direction 77 causes armature 10 to contact the tip of contact 34 closing circuit A and opening circuit B. The circuit A now remains latched in the closed position until the actuator is once again displaced in the direction 76.

FIG. 8 illustrates an alternative method of construction of the stationary contacts associated with capsule. Here instead of a platinum conductor running the length of the capsule, the stationary contact is provided as a platinum disc which is mercury wettable and attached to and protruding from the nonmercury wettable tantalum disc. The annular opening 78 of the control core 79 is retained for purging the hermetically sealed, contact enclosing chamber and filling it with a desirable gas. To this end the opening may extend into the chamber through a grooved passage as shown.

The invention has been described herein in connection with a preferred embodiment, but various changes may be made in the details of construction and in the manner of fabrication without departing from the principles and spirit of the invention as defined in the appended claims.

What I claim as new and desire to be secured by Letters Patent of the United States is:

l. A mercury-wetted electrical contact capsule comprising,

a. a flat, flexible, magnetic spiral spring armature having its major surfaces, including a central contact area thereof, wet by mercury,

. a pair of flat magnetic rings having their inner faces wet by mercury and securing between them the periphery of said armature,

c. respective outer tubular members abutting said rings and each forming a cylindrical extension of one of said rings,

. an inner tubular magnetic core extending coaxially within each of said outer tubular members, each of said cores having an end surface not wet by mercury confronting at least the central contact area of said diaphragm,

e. a ceramic seal between each outer tubular member and its corresponding inner tubular core to form with said rings and the opposite seal a hermetic contact chamber, and A a contact wire passing through each inner tubular core and projecting therefrom towards said diaphragm; the end face only of said contact wire adjacent said diaphragm being wet by mercury.

2. A capsule in accordance with claim 1, and an operating winding surrounding the portion of at least one of said inner magnetic cores which extends distally beyond said ceramic seals.

3. A capsule in accordance with claim 1, the distal ends of said inner magnetic cores being hermetically sealed to said contact wires.

4. A capsule in accordance with claim 1, and an atmosphere of hydrogen gas within said chamber.

5. A capsule in accordance with claim 1, and a casing sleeve surrounding said outer tubular members and said rings, and hermetically sealed to the former.

6. A capsule in accordance with claim 1 in which said wires are chrome-plated platinum, and the tip of the contact wire passing through each inner tubular core is constituted by an exposed mercury-wettable platinum surface, the remainder of said wire being nonwettable.

7. A mercury-wetted contact capsule comprising a concentric magnetic structure including a central core of tubular configuration, a glass-to-metal seal of annular shape surrounding and sealed to said core adjacent one end thereof. an outer sleeve surrounding and sealed to said glass-to-metal seal, a flexible contact disc spaced from an end of said sleeve adjacent said seal by a peripheral ring, and a contact wire projecting from said central core toward said disc; the surface of said disc, the inner surface of said ring, and the tip of said contact wire being mercury wetted.

8. A capsule in accordance with claim 7 in which said central core is of magnetic material capable of being mercury wetted, and a layer of nonwettable material on the end face of said core facing said contact disc.

9. In a mercury-wetted switch, a cylindrical contact chamber comprising a transverse magnetic disc flexible in a direction normalto the plane of the disc, a peripheral ring engaging the margin of said disc and forming one peripheral wall of said chamber, a coaxial metallic sleeve forming an extension of said ring, a glass element sealed to and across said sleeve, a central magnetic core sealed in and protruding through said glass element toward said diaphragm, and a contact wire protruding through said core toward said diaphragm; said diaphragm, said ring and the tip end surface only of said wire being mercury wetted.

10. The method of fabricating a mercury-wetted contact capsule, comprising mercury wetting a slotted flexible contact disc, at least the inner surfaces ofa pair of magnetic rings, and the contact tip surfaces of a pair of coaxially related tubular subassemblies of an inner tubular magnetic core glass sealed within an outer metallic tube, said contact tip surfaces projecting through said inner magnetic cores; assembling said rings about the margins of opposite major faces of said disc, clamp ing said rings between the coaxially positioned subassemblies, hermetically welding said subassemblies within a common outer sleeve, passing inert gas through one of said tubular cores to flush the space encompassed within said rings and to provide an inert atmosphere surrounding said contacts, and sealing off said tubular cores.

11. A mercury contact capsule comprising a housing, first and second contacts, means for hermetically sealing said first and second contacts across said housing to form an inner hermetically sealed chamber spaced between two outer chambers, a third contact positioned within said inner chamber between said first and second contacts, said first and second contactors being formed of electrically conductive magnetic material fixedly spaced from the chamber wall by a nonconductive, nonmagnetic, nonmercury wettable member and having a mercury wettable contact portion in spaced relationship with said third contact, said third contact being formed of an electric conductive magnetic material shaped in the form of a flat spiral spring supported by said chamber at its periphery and being resilient in the directions of said first and second contacts to make contact therewith under the influence of an applied magnetic force, a reservoir for supplying mercury to wet said third contact by capillary action comprising the peripheral extremities of said second contact and the portion of said housing within said inner chamber being mercury wettable.

12. An arrangement according to claim 11 further comprising magnetic field producing means positioned in each of said outer chambers for selectively driving said third contactor into contact with said first and second contactors.

13. An arrangement according to claim 12 wherein said magnetic field producing means comprises a respective magnetic core extending axially through each outer chamber and comprising the wettable contact portions of said first and second contactors, its end protruding into the inner chamber, and respective magnetic field producing means magnetically coupled to each of said cores.

14. In a mercury wetted switch, a cylindrical contact chamber comprising a transverse magnetic disc flexible in a direction normal to the plane of the disc, a peripheral ring engaging the margin of the disc and forming one peripheral wall of the chamber, a coaxial metallic sleeve forming extensions of said ring in different directions, a pair of spaced apart ceramic elements sealed to and across said sleeve for containing said magnetic disc, respective central cores sealed in and protruding through respective ones of said ceramic elements toward said disc, respective contact conductors protruding through each of said cores toward said disc, said disc, said ring and the tip end surfaces only of said conductors being mercury wetted, means for causing said disc to make contact with the tip end of one of said conductors and breaking contact with the tip end of the other conductor, and means for causing said disc to make contact with the tip end of said other conductor while breaking contact with the tip end of the said one conductor.

15. In a mercury wetted switch, a cylindrical contact chamber comprising a transverse magnetic disc flexible in a direction normal to the plane of the disc, a peripheral ring cngaging the margin of the disc and forming one peripheral wall of the chamber, a coaxial metallic sleeve forming extensions of said ring in different directions, a pair of spaced apart ceramic elements sealed to and across said sleeve for containing said magnetic disc, respective central magnetic cores sealed in and protruding through respective ones of said ceramic elements toward said disc, respective contact conductors protruding through each of said cores toward said disc, said disc, said ring and the tip end surfaces only of said conductors being mercury wetted, a first magnetic circuit comprising one of said cores for selectively driving said disc to make contact with the tip end of one of said conductors and breaking contact with the tip end of the other conductor, and means for a second magnetic circuit comprising the other of said cores for causing said disc to make contact with the tip end of said other conductor while breaking contact with the tip end of the said one conductor, 

1. A mercury-wetted electrical contact capsule comprising, a. a flat, flexible, magnetic spiral spring armature having its major surfaces, including a central contact area thereof, wet by mercury, b. a pair of flat magnetic rings having their inner faces wet by mercury and securing between them the periphery of said armature, c. respective outer tubular members abutting said rings and each forming a cylindrical extension of one of said rings, d. an inner tubular magnetic core extending coaxially within each of said outer tubular members, each of said cores having an end surface not wet by mercury confronting at least the central contact area of said diaphragm, e. a ceramic seal between each outer tubular member and its corresponding inner tubular core to form with said rings and the opposite seal a hermetic contact chamber, and f. a contact wire passing through each inner tubular core and projecting therefrom towards said diaphragm; the end face only of said contact wire adjacent said diaphragm being wet by mercury.
 2. A capsule in accordance with claim 1, and an operating winding surrounding the portion of at least one of said inner magnetic cores which extends distally beyond said ceramic seals.
 3. A capsule in accordance with claim 1, the distal ends of said inner magnetic cores being hermetically sealed to said contact wires.
 4. A capsule in accordance with claim 1, and an atmosphere of hydrogen gas within said chamber.
 5. A capsule in accordance with claim 1, and a casing sleeve surrounding said outer tubular members and said rings, and hermetically sealed to the former.
 6. A capsule in accordance with claim 1 in which said wires are chrome-plated platinum, and the tip of the contact wire passing through each inner tubular core is constituted by an exposed mercury-wettable platinum surface, the remainder of said wire being nonwettable.
 7. A mercury-wetted contact capsule comprising a concentric magnetic structure including a central core of tubular configuration, a glass-to-metal seal of annular shape surrounding and sealed to said core adjacent one end thereof, an outer sleeve surrounding and sealed to said glass-to-metal seal, a flexible contact disc spaced from an end of said sleeve adjacent said seal by a peripheral ring, and a contact wire projecting from said central core toward said disc; the surface of said disc, the inner surface of said ring, and the tip of said contact wire being mercury wetted.
 8. A capsule in accordance with claim 7 in which said central core is of magnetic material capable of being mercury wetted, and a layer of nonwettable material on the end face of said core facing said contact disc.
 9. In a mercury-wetted switch, a cylindrical contact chamber comprising a transverse magnetic disc flexible in a direction normal to the plane of the disc, a peripheral ring engaging the margin of said disc and forming one peripheral wall of said chamber, a coaxial metallic sleeve forming an extension of said ring, a glass element sealed to and across said sleeve, a central magnetic core sealed in and protruding through said glass element toward said diaphragm, and a contact wire protruding through said core toward said diaphragm; said diaphragm, said ring and the tip end surface only of said wire being mercury wetted.
 10. The method of fabricating a mercury-wetted contact capsule, comprising mercury wetting a slotted flexible contact disc, at least the inner surfaces of a pair of magnetic rings, and the contact tip surfaces of a pair of coaxially related tubular subassemblies of an inner tuBular magnetic core glass sealed within an outer metallic tube, said contact tip surfaces projecting through said inner magnetic cores; assembling said rings about the margins of opposite major faces of said disc, clamping said rings between the coaxially positioned subassemblies, hermetically welding said subassemblies within a common outer sleeve, passing inert gas through one of said tubular cores to flush the space encompassed within said rings and to provide an inert atmosphere surrounding said contacts, and sealing off said tubular cores.
 11. A mercury contact capsule comprising a housing, first and second contacts, means for hermetically sealing said first and second contacts across said housing to form an inner hermetically sealed chamber spaced between two outer chambers, a third contact positioned within said inner chamber between said first and second contacts, said first and second contactors being formed of electrically conductive magnetic material fixedly spaced from the chamber wall by a nonconductive, nonmagnetic, nonmercury wettable member and having a mercury wettable contact portion in spaced relationship with said third contact, said third contact being formed of an electric conductive magnetic material shaped in the form of a flat spiral spring supported by said chamber at its periphery and being resilient in the directions of said first and second contacts to make contact therewith under the influence of an applied magnetic force, a reservoir for supplying mercury to wet said third contact by capillary action comprising the peripheral extremities of said second contact and the portion of said housing within said inner chamber being mercury wettable.
 12. An arrangement according to claim 11 further comprising magnetic field producing means positioned in each of said outer chambers for selectively driving said third contactor into contact with said first and second contactors.
 13. An arrangement according to claim 12 wherein said magnetic field producing means comprises a respective magnetic core extending axially through each outer chamber and comprising the wettable contact portions of said first and second contactors, its end protruding into the inner chamber, and respective magnetic field producing means magnetically coupled to each of said cores.
 14. In a mercury wetted switch, a cylindrical contact chamber comprising a transverse magnetic disc flexible in a direction normal to the plane of the disc, a peripheral ring engaging the margin of the disc and forming one peripheral wall of the chamber, a coaxial metallic sleeve forming extensions of said ring in different directions, a pair of spaced apart ceramic elements sealed to and across said sleeve for containing said magnetic disc, respective central cores sealed in and protruding through respective ones of said ceramic elements toward said disc, respective contact conductors protruding through each of said cores toward said disc, said disc, said ring and the tip end surfaces only of said conductors being mercury wetted, means for causing said disc to make contact with the tip end of one of said conductors and breaking contact with the tip end of the other conductor, and means for causing said disc to make contact with the tip end of said other conductor while breaking contact with the tip end of the said one conductor.
 15. In a mercury wetted switch, a cylindrical contact chamber comprising a transverse magnetic disc flexible in a direction normal to the plane of the disc, a peripheral ring engaging the margin of the disc and forming one peripheral wall of the chamber, a coaxial metallic sleeve forming extensions of said ring in different directions, a pair of spaced apart ceramic elements sealed to and across said sleeve for containing said magnetic disc, respective central magnetic cores sealed in and protruding through respective ones of said ceramic elements toward said disc, respective contact conductors protruding through each of said cores toward said disc, said disc, said ring and The tip end surfaces only of said conductors being mercury wetted, a first magnetic circuit comprising one of said cores for selectively driving said disc to make contact with the tip end of one of said conductors and breaking contact with the tip end of the other conductor, and means for a second magnetic circuit comprising the other of said cores for causing said disc to make contact with the tip end of said other conductor while breaking contact with the tip end of the said one conductor. 